California Evidence Code Section 818

818. For the purpose of determining the capitalized value of the reasonable net rental value attributable to the property or property interest being valued as provided in Section 819 or determining the value of a leasehold interest, a witness may take into account as a basis for his opinion the rent reserved and other terms and circumstances of any lease of comparable property if the lease was freely made in good faith within a reasonable time before or after the date of valuation.